The methods of “painting” lines on highways or road markings have changed very little in the past thirty years. Herein the word “painting” refers to any method of applying a coating to a road surface to form a line or road marking. Prior to this invention, there were only three widely used methods to paint lines on highways. The most common technique is to spray a chemical paint on to the road and wait for the paint to dry. The apparatus to spray this paint is typically an “air” or “airless” paint machine wherein the paint is carried by air and projected to the road surface or where the paint the forced through a small hole at very high pressure and projected onto the road surface. The “chemical spray” is the most widely used system to paint lines on highways or road markings.
The second technique to paint lines on highways is to apply a tape to the road surface wherein this tape is bonded to the road surface either with heat or with suitable chemicals. U.S. Pat. No. 4,162,862 illustrates a “Pavement Striping Apparatus and Method” using a machine to press the tape into hot fresh asphalt. U.S. Pat. No. 4,236,950 illustrates another method of applying a multilayer road marking prefabricated tape material.
A third technique is to use a high velocity, oxygen fuel (“HVOF”) thermal spray gun to spray a melted power or ceramic powder onto a substrate. This is shown in U.S. Pat. No. 5,285,967.
Of the three painting methods, the first method of spraying a chemical onto the road surface and waiting for the paint to dry is the predominant technique used today.
The history of line painting indicates that there are at least three properties of “paint” which are important to the highway marking industry: (1) The speed at which the paint dries. (2) The bonding strength of the paint to the road surface. (3) The durability of the paint to withstand the action of automobiles, sand, rain, water, etc.
As discussed in U.S. Pat. No. 3,706,684 (Dec. 19, 1972), the first conventional traffic paints were based on drying oil alkyds to which a solvent, such as naphtha or white spirits was added. The paint dries as the solvent is released by evaporation. However, the paint “drying” (oxidation) process “continues and the film becomes progressively harder, resulting in embrittlement and reduction of abrasive resistance thereof causing the film to crack and peel off.” The above patent describes “rapid-dry, one-package, epoxy traffic paint compositions which require no curing agent.”
As described in U.S. Pat. No. 4,765,773:
“The road and highways of the country must be painted frequently with markings indicating dividing lines, turn lanes, cross walks and other safety signs. While these markings are usually applied in the form of fast drying paint, the paint does not dry instantly. Thus a portion of the road or highway must be blocked off for a time sufficient to allow the paint to dry. This, however, can lead to traffic congestion. If the road is not blocked for sufficient time to allow the paint to dry, vehicle traffic can smear the paint making it unsightly. Also in some instances the traffic will mar the marking to such an extent that the safety message is unclear, which could lead to accidents.”
Low-boiling volatile organic solvents evaporate rapidly after application of the paint on the road to provide the desired fast drying characteristics of a freshly applied road marking.
The U.S. Pat. No. 4,765,773 patent illustrates the use of microwave energy to hasten the paint drying process of such solvents.
While the low-boiling volatile organic solvents promote rapid drying, “this type of paint formulation tends to expose the workers to the vapors of the organic solvents. Because of these shortcomings and increasingly stringent environmental mandates from governments and communities, it is highly desirable to develop more environmentally friendly coatings or paints while retaining fast drying properties and/or characteristics” (U.S. Pat. No. 6,475,556).
To solve this problem paints have been developed using waterborne rather than solvent based polymers or resins. U.S. Pat. No. 6,337,106 describes a method of producing a fast-setting waterborne paint. However, the drying times of waterborne paints are generally longer than those exhibited by the organic solvent based coatings. In addition the waterborne paints are severely limited by the weather and atmospheric conditions at the time of application. Typically the paint cannot be applied when the road surface is wet or when the temperature is below −10 degrees centigrade. Also, the drying time strongly depends upon the relative humidity of the atmosphere in which the paint is applied. A waterborne paint may take several hours or more to dry in high humidity. Lastly the waterborne paints, which are generally known as “rubber based paints”, are made from aqueous dispersion polymers. These polymers are generally very “soft” and abrade easily from the road surface due to vehicular traffic, sand and weather erosion.
The above patents all attempt to solve the paint drying problem when using “waterborne” paints and speeding the drying process. The present invention solves the drying problem by not using any solvents in the “painting process”.
The present invention relates closely to the work done to repair coke ovens, glass furnaces, soaking pots, reheat furnaces and the like which are lined with refractory brick or castings. This process is known today as “ceramic welding”.
U.S. Pat. No. 3,800,983 describes a process for forming a refractory mass by projecting at least one oxidizable substance which burns by combining with oxygen with accompanying evolution of heat and another non-combustible substance which is melted or partially melted by the heat of combustion and projected against the refractory brick. The invention is designed to repair, in situ, the lining of a furnace while the furnace is operating. Typically the temperature of the walls of the furnace is over 1500 degrees centigrade and the projected powder(s) ignites spontaneously when projected against the hot surface. In this process it is extremely important that both the oxidizable and non-combustible particles are matched chemically and thermally with the lining of the furnace.
If the thermal properties are not correct, the new refractory mass will crack off from the lining of the furnace due to the differential expansion of the materials. If the chemical composition is not correct, the new refractory mass will “poison” the melt in the furnace.
In the U.S. Pat. No. 3,800,983 patent the oxidizable and non-oxidizable particles are combined as one powdered mixture. The powder is then aspirated from the powder hopper by using pure oxygen under pressure. The resulting powder-oxygen mixture is then driven through a flexible supply line to a water-cooled lance. The lance is used to project the powder-oxygen mixture against the refractory lining of the furnace to be repaired. The powder-oxygen mixture ignites spontaneously when it impinges on the hot surface of the oven.
The object of the '983 invention and those that followed is to select the composition of the powders to match the characteristics of the refractory lining and to prevent “flashback” up the lance and back towards the operator of the equipment. “Flashback” is the process wherein the oxygen-powder stream burns so quickly that the flame travels in the reverse direction from the oxygen-powder and causes damage to the equipment and serious hazards to the equipment operator.
U.S. Pat. No. 4,792,468 describes a process similar to that above and specifically illustrates the chemical and physical properties of the oxidizable and refractory particles needed to form a substantially crack-free refractory mass on the refractory lining.
U.S. Pat. No. 4,946,806 describes a process based upon the U.S. Pat. No. 3,800,893 patent wherein the invention provides for the use of zinc metal powder or magnesium metal powder or a mixture of the two as the heat sources in the formation of the refractory mass.
U.S. Pat. No. 5,013,499 describes a method of flame spraying refractory materials (now called “ceramic welding”) for in situ repair of furnace linings wherein pure oxygen is used as the aspirating gas and also the accelerating gas and the highly combustible materials can be chromium, aluminum, zirconium or magnesium without flashback. The apparatus is capable of very high deposition rates of material.
U.S. Pat. No. 5,002,805 improves on the chemical composition of the oxidizable and non-oxidizable powders by adding a “fluxing agent” to the mixture.
U.S. Pat. No. 5,202,090 describes an apparatus similar to that shown in U.S. Pat. No. 5,013,499. In the '090 patent, there are specific details about the mechanical equipment used to mix the powdered material with oxygen and transport the oxygen-powder combination to the lance. This apparatus also permits very high deposition rates of the refractory material without flashback.
U.S. Pat. No. 5,401,698 describes an improved “Ceramic Welding Powder Mixture” for use in the apparatus shown in the previous patents listed. This mixture requires that at least two metals are used as fuel powder and the refractory powder contains at least magnesia, alumina or chromic oxide.
U.S. Pat. No. 5,686,028 describes a ceramic welding process where the refractory powder is comprised of at least one silicon compound and also that the non-metallic precursor is selected from either CaO, MgO or FeO.
U.S. Pat. No. 5,866,049 is a further improvement on the composition of the ceramic welding powder described in U.S. Pat. No. 5,686,028.
U.S. Pat. No. 6,372,288 is a further improvement on the composition of the ceramic welding powder wherein the powder contains at least one substance which enhances production of a vitreous phase in the refractory mass.